1. Field of the Invention
The present invention relates to an optical plate for use in, for example, a backlight module, the backlight module typically being employed in a liquid crystal display (LCD).
2. Discussion of the Related Art
In a liquid crystal display device, liquid crystal is a substance that does not itself illuminate light. Instead, the liquid crystal relies on light received from a light source, in order for the liquid crystal to display information. In the case of a typical liquid crystal display device, a backlight module powered by electricity supplies the needed light.
FIG. 15 represents a typical direct type backlight module 100. The backlight module 100 includes a housing 101, a light reflective plate 102, a light diffusion plate 103, a prism sheet 104, and a plurality of light emitting diodes 105 (hereinafter called LED). The housing 101 includes a rectangular base 1011 and four sidewalls 1013 extending from a periphery of the base 1011. The base 1011 and the four sidewalls 1013 cooperatively define a chamber 1017. Each LED 105 includes a base portion 1053 and a light-emitting portion 1051 disposed on the base portion 1053. The LEDs 105 are electrically connected to a printed circuit board 107, and the printed circuit board 107 is fixed to the base 1011 of the housing 101. The light reflective plate 102 is disposed on the LEDs 105 in the chamber 1017. The light reflective plate 102 defines a plurality of through holes (not labeled) that allows the light-emitting portions 1051 of the LED 105 to pass through and to emit light to be transmitted to the light diffusion plate 103. The light diffusion plate 103 and the prism sheet 104 are stacked in that order on the chamber 1017. Light emitted from the LEDs 105 is substantially reflected by the light reflective sheet 102 to enter the light diffusion plate 103, and diffused uniformly in the light diffusion plate 103, and finally surface light is outputted from the prism sheet 104.
Generally, a plurality of dark areas may occur because of a reduced intensity of light between adjacent LEDs 105. In the backlight module 100, each LED 105 further includes a reflective sheet 106 disposed on the top of the light-emitting portion 1051, configured for decreasing the brightness of a portion of the backlight module 100 above the LED 105. However, the brightness of the backlight module 100 is still non-uniform. One method of enhancing the uniformity of brightness of the backlight module 100 is to increase the space between the light diffusion plate 103 and the LEDs 105. This increase in space tends to eliminate dark areas. However, increasing the space between the diffusion plate 103 and the LEDs 105 will also increase the thickness of the backlight module 100, and the further overall intensity of the output light rays is reduced.
What is needed, therefore, is a new optical plate and a backlight module using the optical plate that can overcome the above-mentioned shortcomings.